linux-kernel - Re: [RFC PATCH 0/3] GPIO support on the Etron EJ168/EJ188/EJ198 xHCI controllers

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Message-ID: <CACRpkdZdAs_FK8NU+KE5hZBVTZ-fBRDi7=zn0PqxZhPJR+zxwA@mail.gmail.com>
Date:   Wed, 7 Oct 2020 11:17:41 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-usb <linux-usb@...r.kernel.org>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, systemchip@...on.com
Subject: Re: [RFC PATCH 0/3] GPIO support on the Etron EJ168/EJ188/EJ198 xHCI controllers

On Sun, Oct 4, 2020 at 8:00 PM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:

> The goal of this series to add support for the GPIO controller on the
> Etron EJ168/EJ188/EJ198 controllers.

This overall is a fine driver, but have you considered the option of just
implementing the GPIO chip in drivers/usb/host/xhci-pci.c?

There are several USB serial adapters that have a GPIO chip
embedded and we just add the GPIO chip into the serial driver.
I have done the same with some networking switches. It is
perfectly fine for drivers outside of drivers/gpio to occasionally
define a minor GPIO chip if GPIO is not their primary function.

Please consider simply activating the XHCI driver and make it
instantiate a GPIO chip if it happens to be an
EJ168/EJ188/EJ198 controller.

Yours,
Linus Walleij